The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
IEEE 802.11-2012, IEEE 802.16-2009, and IEEE 802.20-2008, which are hereby incorporated by reference in their entirety, define operation and implementation of wireless networks including wireless local area networks (WLANs). These standards define modes of operation for WLANs, including ad-hoc and infrastructure.
FIG. 1 illustrates a functional block diagram of an ad-hoc wireless network 100. The ad-hoc wireless network 100 includes three wireless client stations 104-1, 104-2, and 104-3 (collectively, client stations 104), although ad-hoc networks with two or more client stations are possible. The client stations 104 together form a basic service set (BSS), identified by a BSS identifier (BSSID). In an ad-hoc network, such as the ad-hoc wireless network 100, the client stations 104 communicate directly with each other as indicated by the arrows in FIG. 1.
A beacon is periodically transmitted by the client stations 104. The beacon includes a timestamp used for synchronization, a beacon interval, and capability information—such as supported transfer rates. After transmission of the beacon, there is an announcement traffic indication message (ATIM) window, and a length of the ATIM window is indicated by the beacon. During an ATIM window, a first client station 104 can notify a second client station 104 that the first client station 104 has buffered traffic ready to be sent to the second client station 104.
A beacon interval specifies an amount of time before a next beacon will be transmitted. Based upon the beacon interval, client stations 104 can operate in a low power mode until the next beacon is expected. During low power mode, a client station 104 may power down components, such as transceivers, and/or otherwise alter operation to conserve power.
A client station 104 may not be able to transmit or receive data while in low power mode. Therefore, a client station 104 resumes normal operation in order to receive a beacon, and will remain awake during an ATIM window. If a client station 104 receives or transmits based on a notification received during an ATIM window of a beacon interval, the client station 104 will stay awake for a remainder of the beacon interval.
FIG. 2 illustrates a functional block diagram of an infrastructure mode wireless network 150. The infrastructure mode wireless network 150 includes three client stations 154-1, 154-2, and 154-3 (collectively, client stations 154), which all communicate with a common device, access point (AP) 156.
The client stations 154 and the AP 156 together form a BSS. In various implementations, the BSSID corresponds to the MAC address of the AP 156. The AP 156 serves as an intermediary for communications between the client stations 154. The AP 156 may also communicate with a wired network 158, which in turn may communicate with other BSS's (not shown) or other networks, such as the Internet 160.
The AP 156 periodically transmits a beacon to the client stations 154 within the BSS. The beacon is a packet or frame of information that informs the client stations 154 about the capabilities of the BSS, and coordinates communication within the BSS. The beacon includes the BSSID, the beacon interval, and a delivery traffic indication message (DTIM). The DTIM serves a function similar to the ATIM of an ad-hoc network.